This invention is in the field of petroleum and ground water engineering. More specifically, it is in the field of operation and maintenance of wells, including oil wells, gas wells and water wells of all types.
Some of the problems or irregularities encountered with wells, include, but are not limited to, the following:
Stuck tools or equipment ("fish") in the well. PA1 Closed vs. open perforations. PA1 Casing damage in the form of local collapse or shearing that causes a change in the cross-sectional area Of the well. PA1 Casing damage in the form of corrosion or breakage that causes a widening of the diameter of the interior of the well. PA1 A break in the casing that causes the fluid in the well to be hydraulically coupled with the fluid surrounding and outside of the well. PA1 The contact between two dissimilar fluids in the well, e.g. oil above water. PA1 Zone(s) at which there is no cement bonding the casing to the surrounding formation rock, causing the casing to be more compliant than in other locations where it is supported by cement. PA1 Zones at which fractures or highly permeable material intersect the well. PA1 Zones which, in an uncased well, have been washed out, caved in or otherwise enlarged with respect to the normal well diameter. PA1 The bottom of the open portion of a well that has been partially filled with debris (e.g., sand, mineral scale, pieces of metal). Older methods require the lowering of a wire line into the well to find the bottom. The present method finds the bottom quickly and effectively, without lowering anything into the well. PA1 If a tool has recently become stuck in the well and a high-impedance reflector has been found, one can reasonably conclude that the depth to this reflector is the depth to the tool. PA1 If wells in a certain vicinity are known to fail by casing narrowing or shearing, and if a high-impedance reflector has been found, one can reasonably conclude that the depth to this reflector is the depth to the point of casing damage. PA1 If the boundary between low-density oil floating on higher-density salt water in a well is sought, and if a low-impedance reflector has been found, one can conclude that this is the depth to the boundary. PA1 If a well has been logged and been found to be in good condition, but it is suspected that a section of casing has no cement behind it, the method of the invention can be used to find this section by finding a low-impedance reflector. PA1 1. Systematically using the resonant properties of a well to characterize well features. This is a great advance over conventional methods, which rely on time-consuming and expensive wireline logging methods and diffusive pressure analysis (e.g. pressure transient analysis). PA1 2. Differentiating features of interest from known features that are not of interest. This is done by separating and identifying the various resonant frequencies present in any well. The known resonances are then discarded. The remaining resonances are analyzed to obtain the needed information. PA1 3. Distinguishing high-impedance from low-impedance features. This allows differentiating a well enlargement from a well narrowing, a stuck tool from a poorly cemented section of casing, an oil-water contact from a section of well narrowed by a coating of scale, etc. PA1 4. Evaluating the cross-sectional area or the wavespeed characteristics of downhole features. PA1 5. A full methodology which includes how to acquire the data and how to interpret the data. PA1 6. A methodology usable whether the bottom of the well is open, closed, or partially open, or whether the wellbore is cased, uncased, or partially cased, or whether the wellhead is open, closed, or partially open. PA1 7. A methodology usable with both liquid and gas-filled wells. PA1 8. A methodology usable with wells filled with a plurality of fluids such as oil and water.
The prior art methods of dealing with the above listed problems typically include well-known methods such as wireline logging and lowering into the wellbore of special tools to obtain information or samples of materials. All these methods have in common the need to send special equipment down the wellbore, during which time the well must be out of operation. Moreover, with regard to some of these well problems, there is no prior art method to obtain definitive information as to the exact nature or location of the problem. This lack of a definitive method results in an expensive and time-consuming trial-and-error approach to solving some of the typical well problems.
Copending applications Ser. No. 06/841,645 now U.S. Pat. No. 4,802,144, issued Jan. 31, 1989 and, Ser. No. 06/841,644 now U.S. Pat. No. 4,783,769, issued Nov. 8, 1988 describe methods somewhat related to that of the present application. However both these Applications disclose methods for analyzing features external to the well such as hydraulic fractures. In contrast, the present application discloses a method of dealing with features that are in or immediately adjacent to the wellbore.